Incrementing drive for rotary print wheel in on-the-fly printers



April 14, 1970 R. HARPER 3,505,950

INCREMENTING DRIVE FOR ROTARY PRINT WHEEL IN ON-THE-FLY PRINTERS Filed Jan. 15, 1968 2 Sheets-Sheet 1 INVENTOR LEONARD ROY HARPER ATTORNEY April 14, 1970 DISPLACEMENT L- R. HARPER INCREMENTING DRIVE FOR ROTARY PRINT WHEEL IN ON-THE-FLY PRINTERS Filed Jan. 15, 1968 2 Sheets-Sheet 2 MOTOR CONTROL SINGLE-SHOT DIFFERENTIATOR OPTIMUM TORQUE HIGH TORQUE LOW TORQUE fi SINGLE SHOT T DIFFERENTIATOR I I a SAMPLE PULSE INCREMENTING Claims I ABSTRACT OF THE DISCLOSURE An incrementing drive for a printer comprising two print drums. each attached .tOtzllhE end of a torsion shaft. A drive means is provided to continously drive thetorsion shaft in the middle-A magnetic detent means is provided at each end of the shaft so that the speed of the print-drum is alternately retarded and advanced to accomplish a dwell over a substantial period of time. A plurality of print hammers is selectivelyactuable at. the dwell time to print a character. The current I to the magnetic detent means is monitored and a signal generated in response to the current is utilized to control the torque produced lby the drive means so that the proper dwell characteristics of the print drums are maintained.

BACKGROUND OF THE INVENTION =This invention relates generally to an improved incrementing motion device and more particularly to an incrementing motion device having a'rotatable drive means operable to oscillate a member'about its axis 'while'it is being continuously rotated. There has been described in the prior art'an intermittent motion apparatus comprising a drive motor to continuously drive a rotatable shaft at one point andto provide an electromagnetic detenting device in conjunction with a flywheel to produce an intermittent'motion on the shaft. This device produces advantages in driving relatively heavy loads'at a fairly high ratet'flowever, the device also has-' the disadvantages of requiring'a'heavy flywheel and requiring a'rather complex servo-system to control the speed ofthe drive motor.

'3 Itis therefore'an object of this invention to provide an improved incrementing drive having'the capability of drivinga substantial-load while eliminating thedisdvantages of prior art devices. It'is another object of this inventionto provide an improved incrementing drive for-a drum printer which requires'no more space than conventional drum printers.

It is still another object of thisinvention to provide an improved drum printer which utilizes a simple torque control circuit. I v I I SUMMARY OF THE-INVENTION Brietly,accor ding to th'e invention, there is shownan incrementing device where the driven membensuch. asa print drum for example, is driven in a combination of harmonic motion and linear motion so that during a period of time there is relatively zero motion of the driven membenThis isaccomplished by providing a continously operating drive means for driving an input shaft. A magnetic detent means is mounted at a spaced position on the shaft to alternately retard and advance the shafts rotation due to torsional oscillation to create a dwell for a substantial part of a cycle. A'means for sensing the current through the magnetic detent means is provided and aisigml is generatedin're'sponse to the sensing means to control the drive means tom'aintain'the dwell at the desired point in'the cycle so that autilization operation, such as selectively energizing print hammers, can be'condu'ctedon a cyclicbasis;

United States Patent ments of the'invention as illustrated V 'BRIEF DESCRIPTION OFITHE DRAWINGS FIGURE 1-is a perspective view of a drum printer mechanism embodying the invention; v FIGURE 2 is a longitudinal section view of the printer mechanism shownin FIGURE 1;

FIGURE 3 is a plot of time vs; displacement for a point on the print drum for a typical cycle of oscillation;

FIGURE 4 is a diagrammatic schematic view of the torque control circuit for thedrive means shown in FIG- URE 1;

FIGURE 5 is a plot of the waveforms shown at various points in the circuit of FIGUREv 4. I 1

The foregoing and other objects, features and advanw tages of the invention will be apparent from the following more particular description of the prefer-red embodi in the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS I Referring to the drawings, the incrementing motion device is shown and described in connection with a specific embodiment showing the incremental motion device uti-' lized for a drum printer application, although it will be obvious to those skilled in the art that the use of this device is not so limited, but is applicable to other uses requiring an incrementing motion drive.

The incrementing motion device comprises a shaft 10 which is coupled to be driven by drive means 12. Drive means 12 provides continuous rotation to shaft 10 and a magnetic detent means 14 is provided to alternately retard and advance the end of the shaft to which it is attached. To accomplish this operation, the portion of the shaft between the drive point for drive means 12 and the attachment of the magnetic detent means is flexed in torque, first in one direction and then the other. The result of this flexing of shaft 10 is that the linear motion from the drive means has added to it the harmonic motion caused by the flexing of the shaft so that a dwell in the rotation ofv the utilization device is produced as is shown in FIGURE 3. A sensing means (see FIG 4) is provided to monitor the change in reluctance in magnetic detent means 14 and to generate a signal representative of the change. The signal thus generated is coupled to control the torque produced by drive means 12 thereby to selectively control the dwell characteristics provided by the incremental motion device in driving a utilization device 15.

The driving means for the printer comprises drive motor 12 which is coupled by suitable means such aspulleys 22 and 24 and belt 26 to-continuously drive shaft 10. Shaft 10 is mounted forrotation through suitable bearin'gs 50, 52 in stationary support members 54, 565The bearings associated with the printer are preferably sleeve bearings since the oscillation of the members may damage ball, bearings. The utilization device 15 which is driven by shaft 10 in the embodiment shown inthe drawings comprises a print cylinder. To provide a flywheel type of operation in a space no greater than that required for. a

conventional drum printer, the .print cylinder comprises two cylindrical sections 28L, 28R. I

Each of print drums 28L, 28R is fixed at its outer'end to a mounting means 32L, 32R. Mounting means 32L, 32R are fixed to shaft 10 near itsends. The inner ends of each of type drums 28L, 28R are supported for rotation independent of shaft 10 by means ofbearings 34. Since it is desired to have each of the'print drums 28' oscillated individually on shaftv 10,'the' shaft is'driven from the" middle by spokes 30 which extend through-fixed mounting device 32L for print drum 28L.

The magnetic detent means 14 comprises a soft iron toothed wheel 36 fixedly mounted to shaft 10 at the outer end of each print drum 28L, 28R. A stationary member 38 having a plurality of toothed portions 40 which match the pitch of the teeth portions of wheel 36 is mounted at the end of each of the type drums so that only running clearance is present between the respective teeth portions. A coil 42 is provided for establishing a magnetic field across the gaps between the stationary and rotating toothed portions when coil 42 is energized with a suitable voltage source. A magnetic field can also be achieved by fabricating the stationary member from a permanent magnet material if desired. As will be explained in more detail later, the magnetic detent means produces a torsional vibration in shaft so that a dwell is produced in the motion of print drums 28L, 28R. Applicant has discovered that the maintenance of the proper dwell characteristics can be achieved without the use of a complex motor speed control servo-system. This is accomplished by controlling the torque supplied to shaft 10 by drive motor 12. The torque can be controlled by sensing the change in flux in the magnetic detent means. The current through coil 42 is proportional to the flux change in the circuit.

A print drum of known rotational inertia can be caused to oscillate by driving it through a flexible shaft and alternately retarding and advancing its rotation by a magnetic detent means. If the drum is driven at constant torque, the drum will accelerate to the point where the time it takes to travel one period of the magnetic detent means equals the period of oscillation of the drum. At this point the drum will lock in and will not increase in speed until several times as much torque is applied. Thus, there results a motion on any point on the periphery of the print drum which is a combination of the linear motion from the drive and the harmonic motion caused by oscillation of the drum. The characteristics of the system can be chosen so that there is relatively zero motion for a substantial part of a cycle. This is a valuable characteristic in an on-the-fiy drum printer since a substantial part of the cost of such a printer is devoted to obtaining the required precision in operation of the print hammers and their current driver circuits to prevent smearing or poor vertical registration of the printing. The dwell characteristic enables the use of lower precision (and thus much less costly) print hammers and drivers to obtain a specified printing rate and quality. Alternatively, a higher printing rate at the same quality can be achieved by using the same print hammers and drivers.

The characteristic of the system that once the system starts to oscillate at the natural frequency the drum will ,lock in has already been discussed. Atthis time an increase in torque applied to the system serves to increase the amplitude but not the frequency of the oscillations. Since control of the amplitude of the oscillation is important from the standpoint of producing the desired dwell characteristics, the control of the torque produced by the driving means is important.

. The torque of the driving means can be monitored by sensing the wave shape in the magnetic detent means. The wave shape of the current waveform for various torque conditions is shown in FIGURE 5. The first three waveforms in FIGURE 5 show waveforms for the optimum torque, for a high torque condition and for a low torque condition. These waveforms are obtained by sensing' the current through coil 42. To detect the torque condition it is necessary to sense the level at the point L on the waveform. In the embodiment shown in FIGURE 4 this is accomplished by providing a single shot multivibrator 44 which is turned on at a predetermined time in the waveform such as the positive peak of the waveform for example, and providing a period for single shot 44 equal to the time required to reach point L of the waveform. The output of single shot multivibrator 44 is coupled to a differentiating circuit 46 and the positive portion of the waveform which corresponds to a spike at the fall of the single shot output voltage is coupled to the base of transistor 48 to turn the transistor on. A pulse is produced at the collector 480 of the transistor and this pulse is coupled to one section 58 of a coil. The other section 60 of the coil is center-tapped and this section is coupled in the circuit to coil 42. The sample pulse forward biases the diodes 62, 64 so that the vlltage then appearing at the center tap point of coil 60 in the circuit is applied to the input terminals of the motor control circuit 66. In cases wherev motor 12 is an AC. motor, the signal at the center tap of coil 60 is coupled to the control winding of a saturable reactor to control the voltage to the motor. In the case where motor 12 is a DC. motor, the signal can be used to control the field voltage if a rapid response is not required. If a rapid response is required, the signal is utilized for armature control of the motor.

Print drums 28L, 28R are arranged so that the same type character appears in all print positions to be printed for all positions along the print line. The teeth on wheels 36 are spaced the same distance as the type characters on the drum so that by sensing the positions of the teeth on thewheel a signal is obtained which designates to the control means 20 that a character is in print position. The control means 20 may comprise the processor of a data processing system. The control means has means for storing coded data representing the characters to be printed for each of the print positions. The character then in print position is compared with the coded data representing the character to be printed at that position. On an equal compare a signal is generated which is coupled to energize the print hammer for the selected position. Any suitable type of print hammer may be utilized which is selectively actuable in response to an electrical signal. In the embodiment shown the print hammer comprises a hammer portion 29 which is pivoted for movement to print position by the force of a spring member 31. A hold magnet 33 is provided to hold all the print hammers in the inoperative position and a control magnet 27 is provided for each print hammer. For actuation of a selected print hammer a control signal is coupled to the corresponding control magnet 27 to produce a flux in opposition to the hold coil flux so that the print hammer is released for operation in response to the force of spring 31. The actuation of the print hammer causes hammer portion 29 to impact ribbon 25 and paper into the selected character on the print drum to print the character at the corresponding position along the print line. Alternatively, ribbon 25 may be omitted and pressure sensitive paper used in the printer. At the end of the print cycle a restore mechanism (not shown) is actuated to return each of the print hammers to the inoperative position. Before this time the current to the control coil is turned off so that only the hold coil is active.

To design an incremental motion device according to the invention the moment of inertia I is calculated using well known relationships available in standard textbooks. (1) (n- 2) To accomplish this the outer radius r and the inner radius r of the print drum must be chosen. Generally, these values are chosen to achieve low moment of inertia.

The natural frequency of vibration of the system f is chosen and by substituting this Value and the 3 and 4 relating to torsional spring constant K and torsional stress 1- and by selecting the angle of twist 0 corresponding to the desired spacing between teeth on wheel 36, the shaft dimensions of d and L can be obtained. For example, a particular device having an oscillation amplitude of .04773 inch and a frequency so that it completes one cycle of oscillation in a linear motion distance of .15

inch has a dwell characteristic so that a point on the drum is stationary within .001 inch for 108 degrees of its cycle substantially as shown in FIGURE 3.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. Aprinter comprising:

a rotatable shaft;

means for cyclicly driving said shaft intermediate the ends;

a type member comprising two parts;

means for mounting a type part on each end of the shaft for rotation therewith;

a first and a second magnetic detent means, one of said detent means being associated with each of said type parts in fixed relationship therewith, each of said magnetic detent means comprising a first and a second magnetic member, said first magnetic member being mounted for rotational movement with said type part and movement relative to said second magnetic member, said second magnetic member being stationarily mounted relative to the first magnetic member and in close confronting relation therewith, said magnetic members being shaped to produce cyclic variations in the reluctance of the magnetic path during said relative movement;

means for producing a magnetic flux linking said first and second magnetic members to oscillate the shaft and type member thereon to create a dwell in the rotational movement of each of said type parts for a substantial part of a cycle of oscillation;

-a plurality of print hammers; and

means for selectively energizing said print hammers at the dwell time of each cycle of oscillation.

2. The printer according to claim 1 additionally comprising:

means for generating a signal representative of the variation in current relative to a predetermined reference current due to the change in reluctance in the magnetic path between said magnetic members; and

means for coupling said signal to said means for cyclicly driving said shaft to control the torque thereof.

3. The printer according to claim 1 wherein said magnetic detent means comprises a toothed wheel mounted for movement with said type member;

a stationary toothed member; and

means for generating a magnetic field extending through said toothed members.

4. An incremental motion drive comprising:

a torsion shaft member having a drive portion and a utilization portion;

a driven member coupled to the utilization portion of said shaft member for rotation therewith;

a driving means coupled to said drive portion of said shaft member for continuously driving said driven member;

a magnetic detent means coupled to said shaft member adjacent said utilization portion in fixed relationship therewith, said magnetic detent means comprising a first and a second magnetic member, said first magnetic member being mounted for rotational movement with said driven member and movement relative to said second magnetic member, said second magnetic member being stationarily mounted relative to the first magnetic member and in close confronting relation therewith, said magnetic members being shaped to produce cyclic variations in the reluctance of the magnetic path during said relative movement;

means for producinga magnetic flux linking said first and second magnetic members to oscillate the shaft and said driven member thereon to create a dwell in the rotational movement of said driven member for a substantial part of a cycle of oscillation;

means for generating a signal representative of the variation in current relative to a predetermined reference current due to the change in reluctance in the magnetic path between said magnetic members; and

means for coupling said signal to said driving means to control the torque supplied thereby.

5. The drive according to claim 4 wherein said oscillation occurs at the natural frequency of said drive.

6. A printer for printing characters in a line of spaced print positions along a record medium comprising:

a shaft member mounted for rotary drive;

a type member coupled to said shaft member for mtation therewith; driving means for continuously driving said shaft mem ber; magnetic detent means coupled to said shaft member in fixed relationship with said type member, said magnetic detent means comprising afirst and a second magnetic member, said first magnetic member being mounted for rotational movement with said type member and movement relative to said second magnetic member, said second magnetic member being stationarily mounted relative to the first magnetic member and in close confronting relation therewith, said magnetic members being shaped to produce cyclic variations in the reluctance of the magnetic path during said relative movement;

means for producing a magnetic flux linking said first and said second magnetic members to oscillate said shaft and type member thereon to create a dwell in the rotational movement of said type member for a substantial part of each cycle of oscillation;

means for generating a signal representative of the variation in current relative to :a predetermined reference current due to the change in reluctance in the magnetic path between said magnetic members; and

means for coupling said signal to said driving means to control the torque supplied thereby.

7. The printer according to claim 6 wherein said magnetic detent means comprises a toothed wheel mounted for movement with said type member;

a stationary toothed member; and

means for generating a magnetic field through said toothed members.

8. The printer according to claim 6 additionally comprising a plurality of print hammers; control means for comparing the characters to be printed with the character in print position at the next dwell time and means for selectively energizing said print hammers corresponding to those print positions for which an equal compare occurs at said dwell time of each cycle of oscillation.

References Cited UNITED STATES PATENTS 2,627,807 2/1953 Buhler 101-93 2,898,537 8/1959 Cluwen 31-8-47 X 2,919,641 1/1960 Pfleger 101-93 2,940,386 6/1960 Cetran et al. 101-93 3,049,990 8/ 1962 Brown et al. 101-93 3,148,497 9/ 1964 Clitfor et a1. 310-93 3,216,348 11/1965 Oldenburg et a1 101-93 3,312,887 4/1967 Reese et al 318-47 X WILLIAM B. PENN, Primary Examiner US. Cl. X.R. 

